Natural cheese is the term used in the cheese making art to describe varieties of cheese which are made from various milk sources, such as whole milk and milk adjusted to various fat levels with cream, wherein the milk source is set, either by microorganisms alone or by a combination of microorganisms and a milk coagulating enzyme, such as rennet, and which involves a whey drainage step. Well known examples of natural cheese are Swiss cheese, American-type cheeses, such as Cheddar cheese, Colby cheese, stirred curd cheese, washed curd cheese and the Pasta filata cheeses, such as Mozzarella, Provolone and Scamorze.
In accordance with the present invention, a treated non-fat milk solids substrate is provided which can be used in any of the well known natural cheese make procedures to provide a non-fat natural cheese with texture, taste and organoleptic properties similar to that of natural cheese made with milk containing fat. Typical examples of natural cheese processes are those for Swiss cheese, stirred curd Cheddar cheese and Mozzarella cheese, which are described hereinbelow.
In the manufacture of Swiss cheese, three species of bacteria have conventionally been used as starters during a fermentation period: these being a coccus culture, a rod culture and a propionic acid forming microorganism. Usually, Streptococcus thermophillus is used as the coccus culture; Lactobacillus bulgaricus or Lactobacillus helveticus is used as the rod culture; and Propionibacterium shermanii is used as the propionic acid-forming microorganism. A milk clotting enzyme, such as rennet, is also used and added in an amount such that curd firm enough to cut is formed in about 30 minutes. The fermentation proceeds at a temperature of from about 88.degree. F. to about 94.degree. F. Curd is cut and worked for about 30 minutes to an hour. The curd is then heated over a period of about 30 minutes to a cooking temperature of between 120.degree. F. and 128.degree. F. The curd is stirred at the cooking temperature for about 30 minutes to an hour. The curd is pressed under the whey, and the whey is then removed. The curd is pressed into blocks for curing to produce Swiss cheese with typical eye formation. The time required for fermentation, working and cooking is usually less than 3 hours.
In the manufacture of Cheddar cheese by the stirred curd method, milk is pasteurized at a temperature of 162.degree.-164.degree. F. for a holding time of 16 to 18 seconds. The milk is introduced into a cheese vat and a lactic starter, such as S. lactis, is added to the vat. Fermentation and ripening takes place at a temperature of 87.degree. to 88.degree. F. for a period of about 60 minutes. Rennet is added and coagulation occurs in a further 30 minutes. The curd is cut into particles over a period of about 15 minutes and is then cooked at a temperature of 101.degree. F. to 103.degree. F. for 30 minutes. The curd is stirred out in the whey for a period of 30 to 75 minutes. The curd and whey are then transferred to a drain table, where the whey drains over a period of about 30 minutes. The curd on the drain table is sprayed with water at a temperature of 105.degree. F. for a period of 2 to 4 minutes. Salt is added and the curd is allowed to rest on the drain table for a period of about 10 minutes. The curd is then transferred to a container, usually a 640 pound container, where the curd is pressed under vacuum for a period of 75 minutes. The 640 pound block of Cheddar curd is then transferred to a cooler after a resting period of about 24 hours. The curd is held in the cooler at a temperature of 40.degree. F. for 10 days and is then cured an additional period of 21-45 days at a temperature of 40.degree. F. to 45.degree. F.
Pasta filata cheeses, such as Mozzarella, have traditionally been made by a process wherein the curd is pulled or stretched under hot water or hot whey by use of a paddle or by hand. Modern high production techniques for manufacture of such cheeses, however, utilize an inclined twin auger screw for transporting and stretching the curd under hot water to produce the cheese. In a typical process for manufacture of Mozzarella cheese, milk or partially skimmed milk at a temperature of about 88.degree. F. is acidified to a pH of 5.2-5.5, usually by the addition of acetic acid. The milk is then set to provide a coagulum by the addition of rennet and calcium chloride. The coagulum is cut to provide curd and whey and the curd can be cooked in the whey at a temperature of up to 110.degree. F. The curd is usually stirred in the whey for a period of 15 to 45 minutes. The curd is allowed to settle and the whey is drained. The curd is then milled and transferred to an inclined, twin auger conveyor-cooker, where it is transported and worked under hot water maintained at a temperature of 130.degree. F. to 160.degree. F. over a period of from 30 seconds to 2 minutes. The worked curd is molded into desired shapes, which are then placed in brine for a period of 1-12 hours to provide the Mozzarella cheese. The Mozzarella cheese is then packaged for distribution.
The term "natural cheese" is to be distinguished from the term "processed cheese". Processed cheese generally refers to a class of cheese products which are produced by comminuting, mixing and heating lots of natural cheese into a homogeneous plastic mass. The comminuted cheese is blended and sent to cookers or the like which commonly heat the mass to a temperature of 165.degree. F. to 185.degree. F. During cooking, fat is stabilized with the protein and water by the addition of emulsifying salts, such as citrate or phosphate salts, usually at about a 3% level. The salts cause the protein to become more soluble. Under these circumstances, a stable emulsion of protein, fat and water occurs to provide a smooth, homogeneous mass. The hot mass is packaged directly or formed into slices and packaged. In the United States, Standards of Identity apply to classes of processed cheese and are established by the Food and Drug Administration (FDA). Certain of these classes can contain various additives, such as cream, milk, skim milk, buttermilk, cheese whey and skim milk cheese. The moisture content of processed cheese under the Standards of Identity may range from less than 40% to 60%, and the fat content may range from 20% to 35%. The pH range for processed cheese products typically is between 5.0 and 6.5.
While methods are known for making process cheese from skim milk, there has been substantial technical effort directed to methods for producing a natural cheese from a non-fat milk solids source, such as skim milk. It has been proposed to produce non-fat cheese from skim milk by subjecting the skim milk to membrane processes to increase the solids level of the skim milk, followed by evaporation processes to produce a substrate having the required level of solids to produce a natural cheese. The production of a natural cheese from skim milk, however, is complicated by the fact that the fat is no longer present in the protein matrix. Cheese has a protein matrix which is broken up by fat particles. When the fat particles are not present, the cheese protein matrix becomes very firm and the texture and feel of the cheese is completely different from that normally associated with natural cheese.